Hybrid integrated circuits are used extensively in the electronics industry for various purposes. One of the constituent parts of those devices is a thick film resistor. A thick film resistor is customarily fabricated by screen printing a paste which contains the conductor and resistor onto a substrate such as alumina. The coated substrate is fired at a temperature appropriate to the paste composition. The paste contains at least the following three necessary components; viz., a conducting phase, glass powder to bind the conducting phase and adhere to the substrate, and a vehicle, the latter commonly consisting of an organic polymer and solvent, to provide the proper consistency for screen printing.
Ruthenium dioxide (RuO.sub.2) is widely employed in the industry as one of the conducting phases in thick film resistors, and glass frits having compositions within the PbO--B.sub.2 O.sub.3 --SiO.sub.2 system have frequently constituted the bond. The composition of the frit is formulated to have a coefficient of thermal expansion approximating that of the alumina substrate material. Unfortunately, however, the temperature coefficient of resistance demonstrated by those products has been undesirably high. Hence, the products have exhibited temperature coefficients of resistance in excess of 100 ppm (parts per million).
Therefore, the principal objective of this invention is to develop thick film, RuO.sub.2 -based resistor compositions which can be suitably applied to alumina substrates in the conventional manner, but which manifest low temperature coefficients of resistance, viz., less than 100 ppm and, most preferably, less than 50 ppm.